examples: add example MemFd sink

Add an example of a filter sink that requires MemFd memory on the
input port. Show that it gets automatically mapped and that it contains
MemFd memory.

Fixes #4918

src/examples/audio-dsp-sink2.c

@@ -0,0 +1,186 @@
+/* PipeWire */
+/* SPDX-FileCopyrightText: Copyright © 2025 Wim Taymans */
+/* SPDX-License-Identifier: MIT */
+
+/*
+ [title]
+ Audio sink using \ref pw_filter "pw_filter"
+ [title]
+ */
+
+#include "config.h"
+
+#include <stdio.h>
+#include <errno.h>
+#include <math.h>
+#include <signal.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+
+#include <spa/pod/builder.h>
+
+#include <pipewire/pipewire.h>
+#include <pipewire/filter.h>
+
+struct data;
+
+struct port {
+	struct data *data;
+};
+
+struct data {
+	struct pw_main_loop *loop;
+	struct pw_filter *filter;
+	struct port *in_port;
+	bool move;
+	uint32_t quantum_limit;
+};
+
+/* our data processing function is in general:
+ *
+ *  struct pw_buffer *b;
+ *  out = pw_filter_dequeue_buffer(filter, in_port);
+ *
+ *  .. consume data in the buffer ...
+ *
+ *  pw_filter_queue_buffer(filter, in_port, out);
+ *
+ *  For DSP ports, there is a shortcut to directly dequeue, get
+ *  the data and requeue the buffer with pw_filter_get_dsp_buffer().
+ */
+static void on_process(void *userdata, struct spa_io_position *position)
+{
+	struct data *data = userdata;
+	float *in, max;
+	struct port *in_port = data->in_port;
+	uint32_t i, n_samples = position->clock.duration, peak;
+
+	pw_log_trace("do process %d", n_samples);
+
+	in = pw_filter_get_dsp_buffer(in_port, n_samples);
+	if (in == NULL)
+		return;
+
+	/* move cursor up */
+	if (data->move)
+		fprintf(stdout, "%c[%dA", 0x1b, 2);
+	fprintf(stdout, "captured %d samples\n", n_samples);
+	max = 0.0f;
+	for (i = 0; i < n_samples; i++)
+		max = fmaxf(max, fabsf(in[i]));
+
+	peak = (uint32_t)SPA_CLAMPF(max * 30, 0.f, 39.f);
+
+	fprintf(stdout, "input: |%*s%*s| peak:%f\n", peak+1, "*", 40 - peak, "", max);
+	data->move = true;
+	fflush(stdout);
+}
+
+/* Check the buffer memory */
+static void on_add_buffer(void *_data, void *_port_data, struct pw_buffer *buffer)
+{
+	struct spa_buffer *buf = buffer->buffer;
+	struct spa_data *d;
+
+	pw_log_info("add buffer %p", buffer);
+	d = buf->datas;
+
+	if ((d[0].type != SPA_DATA_MemFd)) {
+		pw_log_error("unsupported data type %08x", d[0].type);
+		return;
+	}
+}
+
+static const struct pw_filter_events filter_events = {
+	PW_VERSION_FILTER_EVENTS,
+	.process = on_process,
+	.add_buffer = on_add_buffer,
+};
+
+static void do_quit(void *userdata, int signal_number)
+{
+	struct data *data = userdata;
+	pw_main_loop_quit(data->loop);
+}
+
+int main(int argc, char *argv[])
+{
+	struct data data = { 0, };
+	uint32_t flags, n_params = 0;
+	const struct spa_pod *params[1];
+	uint8_t buffer[1024];
+	struct spa_pod_builder b;
+
+	pw_init(&argc, &argv);
+
+	data.quantum_limit = 8192;
+
+	/* make a main loop. If you already have another main loop, you can add
+	 * the fd of this pipewire mainloop to it. */
+	data.loop = pw_main_loop_new(NULL);
+
+	pw_loop_add_signal(pw_main_loop_get_loop(data.loop), SIGINT, do_quit, &data);
+	pw_loop_add_signal(pw_main_loop_get_loop(data.loop), SIGTERM, do_quit, &data);
+
+	/* Create a simple filter, the simple filter manages the core and remote
+	 * objects for you if you don't need to deal with them.
+	 *
+	 * Pass your events and a user_data pointer as the last arguments. This
+	 * will inform you about the filter state. The most important event
+	 * you need to listen to is the process event where you need to process
+	 * the data.
+	 */
+	data.filter = pw_filter_new_simple(
+			pw_main_loop_get_loop(data.loop),
+			"audio-dsp-sink2",
+			pw_properties_new(
+				PW_KEY_MEDIA_TYPE, "Audio",
+				PW_KEY_MEDIA_CATEGORY, "Sink",
+				PW_KEY_MEDIA_ROLE, "DSP",
+				PW_KEY_MEDIA_CLASS, "Stream/Input/Audio",
+				PW_KEY_NODE_AUTOCONNECT, "true",
+				NULL),
+			&filter_events,
+			&data);
+
+	flags = PW_FILTER_PORT_FLAG_MAP_BUFFERS;
+
+	spa_pod_builder_init(&b, buffer, sizeof(buffer));
+	params[n_params++] = spa_pod_builder_add_object(&b,
+		SPA_TYPE_OBJECT_ParamBuffers, SPA_PARAM_Buffers,
+		SPA_PARAM_BUFFERS_buffers,  SPA_POD_CHOICE_RANGE_Int(1, 1, 16),
+		SPA_PARAM_BUFFERS_blocks,   SPA_POD_Int(1),
+		SPA_PARAM_BUFFERS_size,     SPA_POD_Int(sizeof(float) * data.quantum_limit),
+		SPA_PARAM_BUFFERS_stride,   SPA_POD_Int(sizeof(float)),
+		SPA_PARAM_BUFFERS_dataType, SPA_POD_CHOICE_FLAGS_Int(1<<SPA_DATA_MemFd));
+
+
+	/* make an audio DSP output port */
+	data.in_port = pw_filter_add_port(data.filter,
+			PW_DIRECTION_INPUT,
+			flags,
+			sizeof(struct port),
+			pw_properties_new(
+				PW_KEY_FORMAT_DSP, "32 bit float mono audio",
+				PW_KEY_PORT_NAME, "input",
+				NULL),
+			params, n_params);
+
+	/* Now connect this filter. We ask that our process function is
+	 * called in a realtime thread. */
+	if (pw_filter_connect(data.filter,
+				PW_FILTER_FLAG_RT_PROCESS,
+				NULL, 0) < 0) {
+		fprintf(stderr, "can't connect\n");
+		return -1;
+	}
+
+	/* and wait while we let things run */
+	pw_main_loop_run(data.loop);
+
+	pw_filter_destroy(data.filter);
+	pw_main_loop_destroy(data.loop);
+	pw_deinit();
+
+	return 0;
+}

src/examples/meson.build

@@ -6,6 +6,7 @@ examples = [
   'audio-dsp-src',
   'audio-dsp-filter',
   'audio-dsp-sink',
+  'audio-dsp-sink2',
   'audio-capture',
   'video-play',
   'video-src',